A Norwegian court sentenced three men to jail on Friday for joining or aiding the Islamic State militant group in Syria, in the first case of its kind in the Nordic region.

Djibril Bashir, 30, and Valon Avdyli, 28, "shall be sentenced for participating in the ISIL terror organization," the Oslo District Court said in its verdict, referring to the Islamic State, which has declared a caliphate in large parts of Iraq and Syria and is active in Libya.

Bashir was sentenced to four years and three months in prison and Valon Avdyli to four years and nine months. A third man, Visar Avdyli, 25, the brother of Valon, was sentenced to seven months in prison for providing aid to the group.

They were sentenced under a new Norwegian law designed to crack down on militants returning from the conflicts in the Middle East, with maximum imprisonment terms of up to six years.

All three men had pleaded not guilty and had argued that the law was enacted only after they left Norway for Syria.

Authorities in Norway, Sweden, Denmark and Finland estimate that hundreds of their citizens may have gone to Iraq or Syria to receive militant training.

Western countries fear that radicalized fighters may come back to launch attacks at home.